Area Forecast Discussion
Issued by NWS Upton, NY

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583
FXUS61 KOKX 260548
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
148 AM EDT Wed Apr 26 2017

.SYNOPSIS...
Weakening low pressure will move slowly up the Mid Atlantic
coast through Wednesday, pass southeast of Long Island Wednesday
evening, and then dissipate east of New England later Wednesday
night. A weakening cold front will approach from the northwest
Thursday and Thursday night, then also dissipate over the area
on Friday. Another cold front will approach from the north
Friday night and Saturday, then presses to the south Saturday
night. The front will then gradually lift north as a warm front,
pushing to the north of the area Monday. A cold front will then
move across Monday night, followed by weak high pressure
building in on Tuesday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Minor adjustments were made based on the latest observations and
near term forecast trends. Pockets of heavier rain will be
confined to eastern LI/SE CT the next several hours, with light
rain/drizzle elsewhere.

Most storm total rainfall amounts ranged from 1/2 to 1 inch with
isolated higher amounts. Brief heavy downpours caused minor
flooding of low lying poor drainage areas.

Low temps tonight will generally be in the lower 50s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
On Wednesday, the stacked low will be slowly moving south and
east of Long Island. Expect scattered showers to continue,
mainly in the morning and especially over Long Island and
southern CT, then tapering off in the afternoon.

The close proximity of the stacked low should keep low clouds
around through the day and possibly some patchy fog, with highs
mainly in the lower 60s.

As the upper low passes just to the SE Wed night, could see some
redevelopment of showers mainly across Long Island mainly after
midnight. Lows will again be in the 50s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Northern stream ridging builds over the area on Thursday keeping
things dry. However, underneath the associated subsidence inversion,
the lowest 100-150 hPa will be fairly saturated, so have increased
cloud cover and decreased temperatures on Thursday. For now
generally going 60-70 across the region, though there is some
potential these could be 5 to maybe even 10 degrees to warm.

A northern stream shortwave passes to the north Thursday night
warranting chance pops over NW 1/3 of the CWA and slight chance pops
elsewhere. With showalters progged to fall to 0 to2, have added
thunder to the forecast as well. Lows Thursday night should be
around 10 degrees above normal.

A northern northern stream shortwave passes by, a little closer
this time, on Friday, warranting chance pops everywhere. Showalter
indices warrant a chance of Thunder.

Note, the GFS is faster than most other solutions with the
associated cold front, so used a non-GFS blend for timing the cold
front and precipitation. As a result, could see locations away from
the coast have highs from the mid 70s to around 80. As a result,
areas mainly west of the Hudson could see CAPES in the afternoon of
around 1000 J/kg along with 40-50 kt of shear so some strong to
severe storms are possible there Friday afternoon.

The region is under quasi zonal flow Friday night-Saturday as
ridging builds to our south and a northern stream trough passes to
the north. Friday night should be dry, but could see some isolated-
scattered showers and possibly a thunderstorm by Saturday
afternoon/evening ahead of a backdoor cold front. Favored the faster
ECMWF timing of the front (based on historical superior ECMWF
handling of backdoor fronts vs. the GFS).

Deep layered ridging builds over the area Saturday night-Sunday
night, then the axis slides to the east on Monday. At the surface,
the back door front pushes well to the South by Sunday morning, then
slowly lifts to the north as a warm front, lifting to the north on
Monday. The surface warm front motion warrants a slight chance of
rain Sunday and a chance of rain Sunday night. There is then a
chance of showers Monday morning and a chance of showers and
thunderstorms Monday, once solidly in the warm sector.

A vigorous northern stream trough approaches Monday night, then
lifts to the north on Tuesday, with its associated surface cold
front pushing through Monday night. As a result, have a chance of
thunderstorms Monday night, then a slight chance of showers Tuesday.

Temperatures Friday-Tuesday were based on the Superblend, with NAM 2-
meter temperatures and a mix down from 975-925 hPa per BUFKIT
soundings added in on Friday. Temperatures should remain well above
normal during this time frame, with Saturday the warmest day - with
highs around 80 in the NYC Metro.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
Low pressure tracks slowly toward the area from the south today.

Generally expect IFR ceilings today. Cannot rule out LIFR/VLIFR
ceilings this morning. Visibilities should remain MVFR to IFR
this morning. During the afternoon, visibilities likely improve
to MVFR or even VFR for a short time before falling again by
sunset.

IFR, LIFR or even VLIFR ceilings and visibilities are forecast
for this evening.

Any heavier rain departs early this morning, with on and off
light rain and drizzle continuing thereafter.

Northeast winds begin to lighten this morning, and speeds of 10
kt or less are expected through much of the day today. Winds
will be light and variable by evening.

.OUTLOOK FOR 06Z THURSDAY THROUGH SATURDAY...
.Late tonight...Potential for LIFR/VLIFR in fog.
.Thursday...IFR/LIFR potential to start...with gradual
improvement to VFR.
.Friday...Chance of MVFR in showers/thunderstorms.
.Saturday...VFR.

&&

.MARINE...
SCA has been dropped for all but the ocean waters.

Winds will gradually diminish overnight. Lingering ocean swells
above 5 ft are likely to continue into at least Wed night.

A relatively relaxed pressure gradient Thursday-Sunday will keep
winds over the waters around Long Island to 15 kt or less.
However, gradually diminishing swells will keep seas over all or
parts of the coastal ocean waters at or above 5 ft through
Friday night. All waters should experience sub-advy conditions
Saturday and Sunday.

&&

.HYDROLOGY...
An additional tenth to quarter inch is possible across eastern
LI/SE CT overnight, with localized higher amounts in any
heavier showers working up from south of LI this morning.

No significant (0.5 inches or more) widespread rainfall is
forecast from Thursday through at least Monday. However,
isolated strong convection could produce locally heavy rainfall
Friday and again on Monday. In areas where this occurs, there is
the potential for the ponding of water on roadways and a very
low chance of minor flooding of known poor drainage areas.

&&

.TIDES/COASTAL FLOODING...
Widespread minor coastal flooding occurred across the lower
NY/NJ Harbor, the South Shore Bays of western Long Island
including Queens and Brooklyn this evening; with locations
along the western Long Island Sound expected to experience the
same through the midnight high tides.

Minor coastal flooding thresholds may be briefly and locally be
exceeded along the southern bays of Western Long Island with the
Wednesday morning high tide. Right now at most it would appear
that a statement could be needed for southern Nassau.

Minor coastal flooding is possible with Wednesday night`s high
tide cycle. Best chances for minor inundation will be at the
south shore back bays of Nassau and Queens, but a statement
could be needed for other areas as minor thresholds have a
chance to just be reached in a few spots. Only 1/3 to 3/4 of a
foot of surge is needed to reach minor flood thresholds Wed
night.

In addition, the elevated water levels combined with a
prolonged period of 5-9 ft breaking surf tonight into Thu will
result in beach erosion issues and may cause some localized dune
toe erosion during the high tides tonight into Wed night.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ350-353-
     355.

&&

$$

UPDATE...DW
AVIATION...PW



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